JPH04149092A - Method and device for controlling growth of cone part - Google Patents

Abstract

PURPOSE:To improve the reproducibility of the shape of a cone part so that the cone part can be shortened by controlling the melt temp. in a Czochralski method so as to attain a target temp. and correcting the target temp. in accordance with the difference between a diameter change rate and the target value thereof. CONSTITUTION:The pulling up and growing of the cone part 32B of a single crystal rod 32 from a melt 16 heated by a heater 14 by the Czochralski method are executed in the following manner: The target value 66 of the temp. relating to this melt 16 and the target value 64 of the diameter change rate of the part where this crystal is grown are preset. The diameter of the part where the crystal is grown is measured and the change rate of this diameter is calculated. The temp. relating to the melt 16 is then measured. The target temp. is corrected in accordance with the difference between the calculated value of the diameter change rate and the target value and the electric power to be supplied to a heater 14 is so controlled that the measured temp. attains the corrected target value.

Description

[Detailed description of the invention] [Fields of industrial use]

The present invention relates to a cone growth control method and apparatus for pulling up and growing a cone of a single crystal rod from a raw material melt using the Czochralski method.

[Conventional technology]

In this type of cone growth control method and device, the diameter is 10
A single crystal is grown by dipping a seed crystal about mm in size into a melt and pulling the seed crystal. That is, the crystal diameter is 3111. [After narrowing down to about 11 to eliminate dislocations, the crystal diameter is increased to grow the desired cylindrical straight body. Since this crystal diameter increasing portion (cone portion) is not used as a product, it is necessary to shorten it as much as possible to reduce the cost of producing a single crystal. However, if the cone portion is made too short, that is, if the crystal diameter is suddenly increased, the crystal becomes disordered and it becomes impossible to grow a straight body portion. Here, if the melt temperature is lowered or the crystal growth rate is lowered, the crystal diameter increases. Although the responsiveness of the crystal diameter change to a change in the crystal bowing rate is considerably faster than the responsiveness of the crystal diameter change to a change in melt temperature, the crystal is easily disordered. On the other hand, if the target shape of the cone section is set, the crystal diameter is measured, and the power supplied to the heater that heats the melt is controlled so as to achieve the target shape, hunting is large and the crystals are Large irregularities are formed on the surface. For this reason, it is necessary to make the inclination of the target shape gentler than the inclination of the ideal shape, which is intended to shorten the cone portion as much as possible, to prevent the crystal from becoming disordered. In other words,
The length of the cone becomes longer than necessary. Therefore, conventionally, a target temperature pattern is set in which the melt temperature decreases with the passage of time, and the power supplied to the heater that heats the melt is adjusted so as to reach this target temperature. According to this control method, since hunting is small, the unevenness formed on the crystal surface is reduced.

[Problem to be solved by the invention]

However, the shape of the cone part depends on the diameter of the cone part, the target diameter of the straight body part, the crystal pulling speed, the pulling shaft rotation speed, the crucible rotation speed, the vertical position of the crucible with respect to the heater, the inner diameter of the crucible, and the melt in the crucible. Since it also depends on the amount etc., it is not possible to obtain a cone shape with good reproducibility. For this reason, it is necessary to make the slope of the target temperature pattern with respect to the elapsed time gentler than the slope of the ideal temperature pattern to make the cone part as short as possible to prevent the crystals from being disordered. The length becomes longer than necessary. In view of these problems, it is an object of the present invention to provide a cone growth control method and apparatus that can improve the reproducibility of the cone shape and shorten the cone.

[Means to solve the problem]

In the present method invention, in a cone growth control method for growing a cone of a single crystal rod by pulling it up from a melt heated by a heater using the Czochralski method, the target temperature (To or T) for the melt is set. +ΔTo) and the target value of the rate of change in the diameter of the growing part of the crystal are set in advance, the diameter of the growing part of the crystal is measured, the rate of change of the diameter is calculated, and the temperature of the melt is determined. Measure the diameter change rate, correct the target temperature based on the difference between the calculated value and the target value, and adjust the power supplied to the heater so that the measured temperature becomes the corrected target temperature. It has steps to Further, in the present device invention, in a cone growth control device for growing a cone portion of a single crystal rod by pulling it up from a melt heated by a heater using the Czochralski method, there is a means for measuring the diameter of the growth portion of the crystal. , means for calculating the rate of change in the diameter, first setting means in which a target value for the rate of change in the diameter is set, means for measuring the temperature of the melt, and a target value of the temperature for the melt. is set, a target temperature correction means for correcting the target temperature based on the difference between the calculated value of the diameter change rate and the target value, and a second setting means for correcting the target temperature based on the difference between the calculated value of the diameter change rate and the target value; The heater has a heater power adjusting means for adjusting the power supplied to the heater. In the method and apparatus invention, the target values for the temperature and the diameter change rate are set as a function of time, pulling length, or diameter. Most preferably, the target value of is set as a function of diameter. Due to this improved reproducibility, the temperature target value is sufficient as a function of time, which is the simplest to construct. The temperature is, for example, the temperature of a recess formed in a heat insulating material surrounding the heater or the surface temperature of the melt. The correction of the target temperature is preferably performed by adding to the target temperature the sum of a proportional component, a differential component, and an integral component regarding the difference between the calculated value of the diameter change rate and the target value. Further, the power adjustment is, for example, an adjustment that performs a PID operation regarding the difference between the measured temperature and the corrected target temperature.

[Action and effect]

In the present invention, without directly controlling the crystal diameter, (1) the melt temperature is controlled to be the target temperature T0, and (2) the diameter change rate ΔD/Δt and its target value are determined, not the diameter itself. value (ΔD/Δt). Based on the difference between the target temperature T. Since this is corrected, the reproducibility of the cone shape can be improved, and thereby the length of the cone can be made shorter than before without causing crystal disturbance.

【Example】

Hereinafter, one embodiment of the present invention will be described based on the drawings. FIG. 1 shows a crystal growth apparatus using the Czochralski method to which a cone growth control apparatus is applied. A silicone polycrystal mass is housed in a quartz crucible 12 fitted into the graphite crucible 10, which is heated and melted into a melt by supplying power to a heater 14 surrounding the graphite crucible 10. Becomes 16. The heater 14 is surrounded by graphite insulation 18, and the components 10-18 are housed within a chamber 20 that is evacuated. The graphite crucible 10 is rotated and raised and lowered in the direction of the arrow by a motor (not shown) via a crucible rotation shaft 22 concentric therewith. on the other hand,
A seed crystal 30 is held above the graphite crucible 10 via a holder 28 at the lower end of a pulling shaft 26 that is concentric therewith. A single crystal 32 is grown by dipping the lower end of the seed crystal 30 in the melt 16 and rotating it while pulling it up in the direction of the arrow. This single crystal 32 is grown in the following order: a narrowed portion 32A for making the crystal free of dislocations, a cone portion 32B for increasing the crystal to the target diameter DB, and a straight body portion 32C having the target diameter DB. A viewing window 36 is provided at the shoulder of the chamber 20 for imaging the bright ring 34 formed at the interface between the single crystal 32 and the melt 16.
is provided, and an imaging device 38 is fixed to the chamber 20 facing the viewing window 36. The composite video signal outputted from the imaging device 38 is supplied to a diameter measuring device 40, and the diameter measuring device 40 measures the diameter of the diaphragm 34 through image processing. On the other hand, in order to measure the temperature of the melt 16, a viewing window 44 is provided on the side surface of the chamber 20, a recess 46 is formed on the side surface of the heat insulating material 18, and the viewing window 44 is configured to allow viewing into the recess 46. A radiation thermometer 48 is fixed to the chamber 20. The target value To of the temperature T detected by the radiation thermometer 48 is determined by the microcomputer 5. As is well known, the microcomputer 50 is
T, J 52, ROM54, RAM56, Hitokaboto 5
8 and an output port 0. The human-powered boat 58 is supplied with a diameter from the diameter measuring device 40 . Further, for example, when the cone section 32A is grown under manual control and then switched to automatic control, a cone section growth start signal is supplied to the human-powered boat 58. A magnetic disk driver 62 and a keyboard 63 are also connected to the input port 58. Via this magnetic disk driver 62, a target diameter burr rate file 64 and a target temperature file 66 are read into the microcomputer 50 and stored in the RAM 56. As shown in the figure, the target diameter change rate file 64 contains a target value (ΔD/Δt) of the rate of change in crystal diameter with respect to time t.
This is a data file in which o is expressed as a function of diameter. Further, the target temperature file 66 contains a target value T of the temperature of the recess 46 as shown in the figure. This is a data file in which t is expressed as a function of time t. The CPU 52 is stored in the ROM 54.
Accordingly, an initial correction value ΔT, which will be described later, is read from the keyboard 63 via the manual boat 58, a diameter is read from the diameter measuring device 40 via the input port 58, and the RAM 56
The corrected target temperature T, with reference to the target diameter change rate file 64 and target temperature file 66 stored in . This target temperature T is calculated. 0, output capo) 60 and D/
It is supplied to a temperature regulator 70 via an A converter 68. The temperature regulator 70 performs, for example, a PID operation so that T is the target temperature T. Power is supplied to the heater 14 via the drive circuit 72 so that the voltage becomes fl. Next, the processing of the micrometer computer 50 will be explained based on FIG. (98) Compare the crystal diameter and arching speed at the end of the constriction section with standard values, and based on these differences, determine the initial correction value Δ1 for the target temperature T. is calculated and input into the microcomputer 50 by operating the keyboard 63. (100) Read the diameter from the diameter measuring device 40 every fixed time Δτ, and take the average value as . (102>Diameter D, determines whether it has reached the set value DA. In order to prevent the single crystal 32 from being disturbed, the DI
<In DA, the target value of the diameter change rate is set to a relatively small value, so the target temperature T. It is thought that there is little need for correction. (104) If D, < [) A, from the target temperature file 66 stored in the RAM 56, time t == i
Target temperature T at Δt. Read out T, +ΔTo as To. shall be. Here, Δt = Δτ. If D, ≧DA, (106) Determine whether the diameter has reached the target diameter D3 of the straight body portion 32C. (108) If D<D, calculate the rate of change ΔD/Δt of the diameter with respect to time. Here, ΔD−(D,
-D,,)7m. (1), O) From the target diameter change rate file 64 and target temperature file 66 stored in the RAM 56, the time t
= Target diameter change rate (ΔD/Δt) at iΔt. and target temperature T. Read out. (112) d, = △D/△t (△D/△t) (1) is calculated. (11,4>To improve the reproducibility of the shape of the cone portion 32B without increasing the unevenness of the cone portion 32B,
Target temperature T. For example, the sum of the proportional component, differential component, and integral component regarding d is calculated as the correction value S.
shall be. In this case, 5=Kpd+KIΣd, △t+
K n△d/△t. Here, K-, K+, Kn are constants selected empirically so that the correction is most effective, and Δ
d = d 1d i-+. (116) T, +ΔTo+S. o. (118) To the temperature controller 70 via the D/A converter 68,
Corrected target temperature T. Supply 0. Then, l is incremented and the process returns to step 100 above. Figures 3 to 5 show the diameter and diameter change rate △D/△t1 when the cone portion 32B was actually grown using this device.
Target diameter change rate (ΔD/Δt)o. Time 1 of target temperature T0 and rotation speed CR of quartz crucible 12
(When 1=0, cone part automatic growth control is started). The test conditions for growing the cone portion 32B are as follows. Quartz crucible 12: Constant vertical position Pulling shaft 26: Constant pulling speed Temperature regulator 70: PIDli moderator Δτ = 6 seconds, Δt = 1 minute, m = 2 DA: 80 mm Da: 158 mm Is m△t short? The selection of mΔt is important because if it is too long, the target temperature T0° will hunt, and if it is too long, the correction will be inaccurate. The preferred range of mΔt was 1 to 3 minutes. In Figures 3-5, the dial value has a linear relationship with temperature. T when t<2 minutes. The reason for the rapid decline is to accelerate the growth rate of the cone. Also, t<2
T0+ΔTokuT in minutes. The reason why it is 0 is as follows. That is, the drive circuit 72 rotates the dial with a motor to adjust the power supplied to the heater 14.
This is because if the rate of change in the target temperature is too large, the rotational speed of this motor will reach the upper limit value and follow-up will be delayed. In Figure 3, the deviation d of the diameter change rate from the target value is D≧
Relatively small in DA. Target temperature T at t-60 to 65 minutes. has been corrected to the + side. In FIG. 4, d becomes relatively large between t-45 and t-50 minutes, and the target temperature T0 is corrected to the + side. At t>50, the integral constant remains as a correction value, and T
o, l! :The slopes of Too are equal. In FIG. 5, since d became negative at t>40, the target temperature T. is corrected to the negative side. Target temperature T. The results of comparing 40 single-crystal rods between the case where the cone part 32B was grown by the conventional method without correcting the temperature T0 and the case where the cone part 32B was grown by the present method in which the target temperature T0 was corrected are as follows. there were. Average value of cone length Conventional method: 1(], '1cm Current method: ], 0.1c
Standard deviation of m-cone length Conventional method: 1.49 This method: 0.65 Defective product incidence (number of dislocations/40) Conventional method: 0.45
This method: 0.10 Note that a defective product refers to one in which the crystal is lowered and melted in the melt due to the occurrence of dislocation, and is pulled up again. The reason why the defect rate is high with conventional force is when the cone length is shortened and the target diameter change rate (ΔD/Δt) is achieved. It is considered that the actual diameter change rate ΔD/Δt became too large in some parts and % dislocation occurred due to the fact that ΔD/Δt was made relatively large and the reproducibility of the surface shape was poor. , - Under severe conditions such as 1-, it is recommended to automatically correct the temperature as in this embodiment. - It was found that the reproducibility of the surface shape was improved and the occurrence of defects was significantly reduced.

[Brief explanation of drawings]

1 to 5 1i 2) An embodiment of the cone growth control method and apparatus according to the present invention, FIG. 1 is a schematic configuration of a crystal growth apparatus to which the cone growth control method and apparatus are applied. FIG. 2 is a flowchart showing the processing procedure of the microcomputer 50 of FIG. 1. 1-1 FIGS. 3 to 5 are diagrams showing the results of actually using the apparatus of this embodiment. In the figure, 10 is a graphite crucible 12 is a quartz pot 14 is a heater 16, a melt 18 is a heat insulating material 201, a J yamba 22 is a crucible rotation axis, 2 is a pulling axis 28, a holder 30 is a seed crystal; 321 is a single crystal 32A is the aperture portion 32F3 is the cone portion 32C is the straight body portion 34 is the bright ring 36.44 is the viewing window 38 is the imaging device 48 is the radiation thermometer 5 (] is the microcomputer 64 is the target diameter change W file 66 is the target temperature file

Claims (1)

[Claims] 1) Cone growth control for pulling and growing a cone (32B) of a single crystal rod (32) from a melt (16) heated by a heater (14) by the Czochralski method. In the method, a target temperature value (66) for the melt and a target value (64) for the diameter change rate of the crystal growth area are set in advance, and the diameter of the crystal growth area is measured (100). , calculate the rate of change in the diameter (108), measure the temperature of the melt, and correct the target temperature based on the difference between the calculated rate of change in diameter and the target value (112-116). A cone growth control method, comprising the steps of: adjusting power supplied to the heater so that the measured temperature reaches the corrected target temperature. 2) A method according to claim 1, characterized in that said setpoint value (64) of said temperature is a function of time and said setpoint value (66) of said diameter change rate is a function of diameter. 3) The method according to claim 1 or 2, characterized in that the temperature is the temperature of a recess (46) formed in a heat insulating material (18) surrounding the heater (14). 4) The correction of the target temperature is characterized in that the sum of a proportional component, a differential component, and an integral component regarding the difference between the calculated value of the diameter change rate and the target value is added to the target temperature. 3. The method according to any one of 3. 5) The method according to any one of claims 1 to 4, characterized in that the power adjustment is an adjustment that performs a PID operation on the difference between the measured temperature and the corrected target temperature. 6), in a cone part growth control device for pulling and growing a cone part (32B) of a single crystal rod (32) from a melt (16) heated by a heater (14) by the Czochralski method; means (38, 40) for measuring the diameter of the growing region; means (50, 108) for calculating the rate of change in the diameter; and first setting means (6) in which a target value for the rate of change in the diameter is set.
4), means (48) for measuring the temperature of the melt, and second setting means (66) in which a target temperature value for the melt is set.
), and target temperature correction means (50, 112 to 1) that corrects the target temperature based on the difference between the calculated value of the diameter change rate and the target value.
16), and heater power adjustment means (7) for adjusting the power supplied to the heater so that the measured temperature reaches the corrected target temperature.
0,72); A cone growth control device comprising: 7), the target value (64) set by the first setting means;
) is a function of diameter, and the target value (66) set by the second setting means is a function of time. 8), the temperature measuring means (48) is connected to the heater (14).
) The device 9) according to claim 6 or 7, wherein the temperature of the recess (46) formed in the heat insulating material (18) surrounding the target temperature correction means (50, 112-116) is detected.
according to any one of claims 5 to 8, wherein the sum of a proportional component, a differential component, and an integral component regarding the difference between the calculated value and the target value of the diameter change rate is added to the target temperature. the method of. 10), the heater power adjustment means (70, 72) adjusts the PI regarding the difference between the measured temperature and the corrected target temperature.
9. Device according to claim 6, characterized in that it is a regulator with a D-operation.